Adobe AUDITION 1.5 - Manual (Page 122)

CHAPTER 4 114
Editing Audio
To change the bit depth of a file:
1 Choose Edit > Convert Sample Type. Alternatively, click the Convert Sample Type
button in the toolbar.
2 Select a bit depth from the Resolution list, or enter a custom bit depth in the text box.
3 When you select a lower bit depth, options in the Dither section are enabled. Set the
following options as desired, and click OK:
Enable Dithering Enables or disables dithering. If dithering is enabled, Adobe Audition
truncates the audio, meaning that unused bits are simply chopped off and discarded. The
result gives a crackly effect that fades in and out on very quiet audio passages.
Dither Depth (Bits) Sets the bit amount of dithering to be applied. In general, values of 0.2
to 0.7 give the best results without adding too much noise. Note, however, that as this value
is lowered, other unwanted harmonic distortion noise appears. (Lower values are usually
okay if you also apply Noise Shaping.)
p.d.f. (probability distribution function) Controls how the dithered noise is distributed
away from the original audio sample value.
Usually, Triangular p.d.f. is a wise choice because it gives the best tradeoff among SNR
(Signal-to-Noise ratio), distortion, and noise modulation. Triangular p.d.f. chooses
random numbers that are generally closer to 0 than to the edges –1 or +1 (that is, the
chance of 0 being chosen is twice as great as the chance of 0.5 or –0.5).
Noise Shaping Determines the placement when you move noise to different frequencies.
The same amount of overall noise is present, but you can place less noise at one frequency
at the expense of placing more noise at another. You may also specify that no noise shaping
is used.
p.d.f. SNR loss Modulation
Rectangular 3 dB Yes
Triangular 4.8 dB No
Gaussian 6 dB Negligible
Shaped Triangular 4.8 dB No
Shaped Gaussian 6 dB Negligible
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